The present invention relates to a process for making an aluminum alloy conductor wire for use in building wire or telephone and telecommunications wire applications.
Copper has been used extensively as the metal in building and communications wire. Aluminum alloys have recently been provided to building and communications wire manufacturers in order to provide wire having weight and economical advantages over copper wire but most of the conductive advantages of copper. This reduction in weight is very desirable because of the distances over which communications wire must be employed and also because of the large number of wires needed in both building and communications wire installations, particularly in large buildings. It is desirable to reduce the weight of such installations, especially considering transportation problems and labor efficiency with heavy wire. Pure aluminum and aluminum alloys, made into wire, as previously proposed, have exhibited disadvantages which tend to restrict the usefulness of such wire for building and communications wire applications. These disadvantages include a lower conductivity than pure copper, processing difficulties, low strength and the tendency for the pure aluminum wire in various connection devices to exhibit stress relaxation. This last disadvantage presents perhaps the most concern regarding the use of dilute aluminum base alloys and pure aluminum in building and communications installations.
It is known that stress relaxation allows a wire to reduce the stress level in time at which the wire is initially installed. Under normal cyclical operating conditions, this undesirable property tends to allow an increase in contact resistance at the connection, thus causing a potentially unsafe condition. Therefore, it is desirable that the resistance of aluminum alloy wire to this stress relaxation phenomenon under either tensile or compressive loading should be quite high since the stability of the entire building or communications installation depends upon continued high conductivity and continuous operative connections.
To be competitive, aluminum alloy wires must also exhibit good strength properties and high ductility. For example, aluminum alloy wire should be capable of meeting minimum communications industrial requirements such as a yield strength of 14 ksi, an ultimate tensile strength of 19 ksi, an elongation of at least 2.5%, a capability of being bent through 180.degree. at least 15 times and a minimum IACS conductivity of 60%. In addition, there should be minimal breaks in the aluminum alloy wire during processing of a 300 lb. sample using standard aluminum wire drawing practices. These requirements for the aluminum alloy wire are all necessary to provide a communications wire which can be pair twisted, then stranded into a multiple strand communications cable, insulated in an extrusion process, and finally reeled and unreeled both before and during installation without breakage of any individual wires. An aluminum alloy wire which meets the above requirements also provides an economical alternative to copper wire. Such an aluminum alloy wire provides a material which can exhibit a high freedom from breakage during drawing and thus a high total production volume. The total production volume is a direct function of the drawing speed and thus freedom from breakage is important as up to an hour may be required to string up a drawing machine if a break occurs, resulting in lost production capacity. It is important to keep the break frequency of the wire down in addition to providing a material which is capable of providing high drawing speeds. This wire should also have sufficient ductility to allow for field installations without wiring breakage.
The major aluminum conductor material which has been used in building and communications wire is Aluminum Association Alloy 1350 or what has more commonly been known as EC aluminum. This material, which contains at least 99.50% by weight pure aluminum, does not satisfy all of the property requirements described above. While AA Alloy 1350 does provide an electrical conductivity of at least 61% IACS, generally desirable percent elongation values have been obtained for AA Alloy 1350 wire only at less than desirable tensile strengths in the wire. Various aluminum alloys have been utilized as alternatives to AA Alloy 1350 but generally do not provide electrical conductivity values as high as the AA Alloy 1350.